The door opening and closing device mounted on the door has the function of enabling the manual opening operation of the door easily and by a small force with use of a biasing force of a compression spring and the function of slowing the opening and closing operations of the door by a damping force of a damper (see PL1).
Such a door opening and closing device has an arm which rotates by opening and closing operations of the door and a runner that is biased by a compression spring to give a biasing force in the opening or closing direction to the arm. The arm and the runner are connected to each other by a link arm which synchronizes rotation of the arm with linear movement of the runner. An end of the link arm is rotatably connected to the runner and the other end of the link arm is rotatably connected to the periphery of the rotation center of the arm. With use of an elastic force of the compression spring, the opening and closing operations of the door can be performed easily by a small force.
The door opening and closing device is provided with a damper for slowing the opening and closing operations of the door. As the damper is used to brake the opening or closing operation of the door based on the elastic force of the compression spring, the door can open and close slowly.
The patent literature 1 (PL1) discloses a door opening and closing device in which a rotary damper is used as the above-mentioned damper and is mounted on the rotation axis of the arm. A one-way clutch may be built in the rotary damper thereby to generate a damping force only in opening or closing of the door.
The patent literature 2 (PL2) discloses an example of using a linear damper. There is provided a neutral range between the opening position and the closing position of the arm, in which range the damping force of the damper is not available. The damping force is set to be generated just before the opening position and closing position of the arm.